1. Field of the Invention
The present invention relates to a toner for electrophotography used for developing electrostatic latent images formed in electrophotography, electrostatic recording method, electrostatic printing, and the like.
2. Discussion of the Related Art
In the heat roller fixing method widely employed as a fixing method for a toner image, the method is excellent in that fixed images having excellent fastness can be obtained at a faster speed, as compared to other fixing methods, and that energy efficiency is high and little harm is caused to the environment by evaporation of a solvent or the like. However, there arises a defect that the offset phenomenon tends to be generated since the toner image is in direct contact with a fixing roller or belt.
On the other hand, from the viewpoint of energy-saving, there have been desired that a waiting time until which the temperature of the fixing device reaches an operable temperature is shortened, and that a toner is fixed at a lower temperature. Therefore, various methods have been tried, including a method of lowering a glass transition point of a resin binder or the like, a method of increasing low-molecular weight components, or a method using a plasticizer or the like. However, there arises a so-called xe2x80x9cblocking,xe2x80x9d wherein the toner is aggregated and solidified during storage or in the developer device.
Therefore, as a method for lowering a fixing temperature, there has been known a toner comprising a crystalline polyester as a resin binder. For instance, Japanese Examined Patent Publication No. Sho 62-39428 discloses a toner comprising a resin binder comprising, a crystalline polyester made from an aromatic polycarboxylic acid component as an acid component, the aromatic polycarboxylic acid component being contained in an amount of 50% by mol or more, and an amorphous polyester made from an aromatic polycarboxylic acid component as an acid component, the aromatic polycarboxylic acid component being contained in an amount of 60% by mol or more. However, when the basic structure of the both polyesters is the same, these resins undesirably become compatible to each other when kneaded during the toner preparation, so that the glass transition point of the crystalline polyester cannot be maintained. In addition, Japanese Examined Patent Publication No. Hei 5-44032 discloses a toner comprising a crystalline polyester having a softening point of from 50xc2x0 to 100xc2x0 C., and a crystalline polyester having a high softening point. However, when the basic structure of the both polyesters is the same, the softening point of the polyester at a lower melting point side has mal-affects to pulverizability and storage stability for the same reasons as above.
An object of the present invention is to provide a toner for electrophotography which is excellent all of the low-temperature fixing ability, the offset resistance, the blocking resistance, and the pulverizability, and capable of maintaining a high level of triboelectric charges for a long period of time, without causing contamination of the photoconductor.
These and other objects of the present invention will be apparent from the following description.
According to the present invention, there is provided a toner for electrophotography comprising a resin binder comprising as its main components:
(a) a crystalline polyester having a softening point of from 85xc2x0 to 150xc2x0 C., obtainable by polycondensing an alcohol component which comprises 80% by mol or more of an aliphatic diol having 2 to 6 carbon atoms and a carboxylic acid component which comprises 80% by mol or more of fumaric acid; and
(b) an amorphous polyester and/or an amorphous polyester-polyamide, obtainable by polycondensing monomers comprising 50% by weight or more of an aromatic compound,
wherein a weight ratio of the crystalline polyester to the amorphous polyester and/or the amorphous polyester-polyamide, i.e. crystalline polyester/(amorphous polyester and/or amorphous polyester-polyamide), is from 1/99 to 50/50.
The toner for electrophotography of the present invention comprises a resin binder comprising a crystalline polyester (Resin A) and an amorphous polyester and/or an amorphous polyester-polyamide (Resin B) as its main components. A total amount of the crystalline polyester and the amorphous polyester and/or the amorphous polyester-polyamide in the resin binder is preferably from 50 to 100% by weight, more preferably from 80 to 100% by weight, especially preferably 100% by weight.
The crystalline polyester used as Resin A is obtained by using monomers containing an alcohol component comprising a dihydric or higher polyhydric alcohol, and a carboxylic acid component comprising a dicarboxylic or higher polycarboxylic acid, an acid anhydride thereof, or an ester thereof. From the viewpoints of the softening point and the crystallinity of the resin, there can be used an aliphatic diol having 2 to 6 carbon atoms in an amount of 80% by mol or more, preferably from 90 to 100% by mol in the alcohol component, and fumaric acid in an amount of 80% by mol or more, preferably from 85 to 100% by mol in the carboxylic acid component. The aliphatic diol having 2 to 6 carbon atoms includes 1,4-butanediol, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,6-hexanediol, neopentyl glycol, 1,4-butenediol, 1,5-pentanediol, and the like. Among them, xcex1,xcfx89-linear alkylene glycols are preferable, and 1,4-butanediol are more preferable.
The dihydric alcohol which may be used other than the aliphatic diol having 2 to 6 carbon atoms includes diethylene glycol, triethylene glycol, 1,8-octanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, hydrogenated bisphenol A, and the like. Among them, aliphatic diols having 7 to 20 carbon atoms, condensates thereof and condensates of the aliphatic diol having 2 to 6 carbon atoms are preferable.
The trihydric or higher polyhydric alcohol includes sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, 1,3,5-trihydroxymethylbenzene, and the like. Among them, from the viewpoints of the softening point and the crystallinity of the resin, glycerol is preferable.
In addition, preferred dicarboxylic acids, acid anhydrides thereof, or esters thereof other than fumaric acid are maleic acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, malonic acid, or a substituted succinic acid of which substituent is an alkyl group having 1 to 20 carbon atoms or an alkenyl group having 2 to 20 carbon atoms, such as dodecenylsuccinic acid and octylsuccinic acid; and derivatives thereof such as acid anhydrides thereof and alkyl(1 to 3 carbon atoms) esters thereof.
The tricarboxylic or higher polycarboxylic acid, an acid anhydride thereof, or an ester thereof includes 1,2,4-benzenetricarboxylic acid (trimellitic acid), 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra(methylenecarboxyl)methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, Empol trimer acid, and derivatives thereof such as acid anhydrides thereof and alkyl(1 to 3 carbon atoms) esters thereof. Among them, from the viewpoints of the softening point and the crystallinity of the resin, trimellitic acid and derivatives thereof are preferable.
In the present invention, in order to form a non-linear polyester as the crystalline polyester, it is desired that trivalent or higher polyvalent monomers, which are selected from the group consisting of trihydric or higher polyhydric alcohols and tricarboxylic or higher polycarboxylic acids, acid anhydrides thereof, or esters thereof, are contained in an amount of from 0.1 to 30% by mol, preferably from 0.1 to 20% by mol, more preferably from 1 to 10% by mol, of all monomers used for polycondensation.
The polycondensation of the alcohol component and the carboxylic acid component can be carried out, for instance, by the reaction at a temperature of from 120xc2x0 to 250xc2x0 C., preferably 150xc2x0 C. or more and preferably 210xc2x0 C. or less, in an inert gas atmosphere, using an esterification catalyst and a polymerization inhibitor as occasion demands. Concretely, in order to enhance the strength of the resin, the entire monomers may be charged at once. Alternatively, in order to reduce the low-molecular weight components, divalent monomers are firstly reacted, and thereafter trivalent or higher polyvalent monomers are added and reacted.
In the present invention, the term xe2x80x9ccrystallinexe2x80x9d means that the ratio of the softening point to the maximum peak temperature of heat of fusion as determined by DSC, i.e. softening point/peak temperature, is 0.9 or more and less than 1.1, preferably from 0.98 to 1.05, and the term xe2x80x9camorphousxe2x80x9d means that the ratio of the softening point to the maximum peak temperature of heat of fusion as determined by DSC, i.e. softening point/peak temperature, is from 1.1 to 4.0, preferably from 1.5 to 3.0.
The crystalline polyester has a softening point of preferably from 85xc2x0 to 150xc2x0 C., more preferably from 100xc2x0 to 140xc2x0 C., and a maximum peak temperature of heat of fusion of preferably from 77xc2x0 to 150xc2x0 C., more preferably from 90xc2x0 to 140xc2x0 C.
The tetrahydrofuran-soluble component of the crystalline polyester has a number-average molecular weight of preferably from 500 to 6000, more preferably from 500 to 5000, from the viewpoints of the blocking resistance and the melt viscosity.
When the crystalline polyester resin comprises two or more resins, it is desired that at least one, preferably all, of the resins are crystalline polyesters described above.
As Resin B, the amorphous polyester and/or the amorphous polyester-polyamide is used. In the present invention, the amorphous polyester is preferable, from the viewpoint of the fixing ability.
The amorphous polyester used as Resin B is obtained by using monomers of known polyhydric alcohol components and polycarboxylic acid components such as carboxylic acids, carboxylic acid anhydrides, and esters thereof.
The polyhydric alcohol component includes alkylene(2 to 3 carbon atoms) oxide(average number of moles: 1 to 10) adduct of bisphenol A such as polyoxypropylene(2.2)-2,2-bis(4-hydroxyphenyl)propane and polyoxyethylene(2.2)-2,2-bis(4-hydroxyphenyl)propane; ethylene glycol, propylene glycol, neopentyl glycol, glycerol, pentaerythritol, trimethylolpropane, hydrogenated bisphenol A, sorbitol, and alkylene(2 to 3 carbon atoms) oxide(average number of moles: 1 to 10) adducts thereof. These polyhydric alcohol components can be used in admixture of two or more kinds.
In addition, the polycarboxylic acid component includes dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, fumaric acid and maleic acid; a substituted succinic acid of which substituent is an alkyl group having 1 to 20 carbon atoms or an alkenyl group having 2 to 20 carbon atoms, such as dodecenylsuccinic acid and octylsuccinic acid; trimellitic acid, pyromellitic acid, and derivatives thereof such as acid anhydrides thereof and alkyl(1 to 8 carbon atoms) esters thereof. These polycarboxylic acid components can be used in admixture of two or more kinds.
In addition, in the preparation of the amorphous polyester-polyamide, in addition to the above polyhydric alcohol component and the polycarboxylic acid component, in order to form an amide component, there are further added polyamines such as ethylenediamine, pentamethylenediamine, hexamethylenediamine, diethylenetriamine, iminobispropylamine, phenylenediamine, xylylenediamine and triethylenetetramine; aminocarboxylic acids such as 6-aminocaproic acid and xcex5-caprolactam; amino alcohols such as propanolamine; and the like. Among them, hexamethylenediamine and xcex5-caprolactam are preferable.
The amorphous polyester and the amorphous polyester-polyamide can be prepared in the same manner as in the crystalline polyester.
In the present invention, as monomers for the amorphous polyester and the amorphous polyester-polyamide, monomers containing an aromatic compound in an amount of 50% by weight or more, preferably from 60 to 95% by weight, are used. By using these monomers, since the basic structure of the crystalline polyester of Resin A is different from that of the amorphous polyester and/or the amorphous polyester-polyamide of Resin B, the properties of the crystalline polyester of Resin A can be maintained, without making Resin A compatible with Resin B when kneaded during the toner preparation.
Preferable aromatic compounds as raw material monomers for the amorphous polyester and the amorphous polyester-polyamide include trimellitic acid and derivatives thereof; isophthalic acid, terephthalic acid and derivatives thereof; alkylene oxide adducts of bisphenol A; phenylenediamine and xylylenediamine; and the like.
It is preferable that each of the amorphous polyester and the amorphous polyester-polyamide has a softening point of from 70xc2x0 to 180xc2x0 C., a maximum peak temperature of heat of fusion of from 50xc2x0 to 85xc2x0 C., a glass transition point of 45xc2x0 to 80xc2x0 C., and a weight percentage of components insoluble to chloroform is from 0 to 50% by weight, respectively. When the amorphous polyester and/or the amorphous polyester-polyamide each comprises two or more resins, it is desired that at least one, preferably all, of the resins is the amorphous polyester and/or the amorphous polyester-polyamide having the properties described above. From the viewpoints of establishing both the fixing ability and the blocking resistance, it is more preferable to use a mixture of a resin having a softening point of from 95xc2x0 to 180xc2x0 C. and a glass transition point of 50xc2x0 to 80xc2x0 C. (Resin a), and a resin having a softening point of from 70xc2x0 to 125xc2x0 C. and a glass transition point of 45xc2x0 to 60xc2x0 C. (Resin b), and that its mixing weight ratio, i.e. Resin a/Resin b, is from 50/50 to 95/5. Here, the glass transition point is a property inherently owned by the amorphous resin and refers to the temperature of an intersection of the extension of the baseline of not more than the glass transition point and the tangential line showing the maximum inclination between the kickoff of the peak and the top of curves.
The weight ratio of the above crystalline polyester to the amorphous polyester and/or the amorphous polyester-polyamide, i.e. crystalline polyester/(amorphous polyester and/or amorphous polyester-polyamide), is 1/99 or more, from the viewpoint of the lowest fixing temperature, and the weight ratio is 50/50 or less, from the viewpoint of preventing hot offset. The weight ratio is preferably from 5/95 to 40/60, especially preferably from 10/90 to 30/70. Incidentally, the crystalline polyester, the amorphous polyester, and the amorphous polyester-polyamide may be each be an independent resin, or a mixture of two or more resins.
It is preferable that the toner for electrophotography of the present invention may further comprise at least one wax. The wax includes natural waxes such as carnauba wax and rice wax; synthetic waxes such as polypropylene wax, polyethylene wax and Fischer-Tropsch wax; petroleum waxes such as montan wax; alcohol waxes; ester waxes; and the like. These waxes can be used alone or in admixture of two or more kinds. Among them, carnauba wax, polypropylene wax and Fischer-Tropsch wax are preferable, from the viewpoint of the compatibility with the resin binder.
It is desired that the melting point of the wax is lower than the softening point of the crystalline polyester by 10xc2x0 C. or more, preferably by 10xc2x0 to 50xc2x0 C., provided that when two or more crystalline polyesters are contained, the softening point to be compared is the softening point of the crystalline polyester having the lowest softening point. The content of the wax is preferably from 0.5 to 10 parts by weight, based on 100 parts by weight of the resin binder.
Further, the toner for electrophotography of the present invention can contain in appropriate amounts additives such as colorants, charge control agents, releasing agents, electric conductivity modifiers, extenders, reinforcing fillers such as fibrous substances, antioxidants, anti-aging agents, fluidity improvers, and cleanability improvers.
As the colorants, all of the dyes and pigments which are used as conventional colorants for toners can be used, and the colorant includes carbon blacks, Phthalocyanine Blue, Permanent Brown FG, Brilliant Fast Scarlet, Pigment Green B, Rhodamine-B Base, Solvent Red 49, Solvent Red 146, Solvent Blue 35, quinacridone, carmine 6B, disazoyellow, and the like. These colorants may be used alone or in admixture of two or more kinds. The content of the colorant is preferably from 1 to 10 parts by weight, based on 100 parts by weight of the resin binder.
The toner for electrophotography of the present invention is preferably a pulverized toner, which can be produced by a kneading-pulverization method, comprising, for instance, homogeneously mixing a resin binder, a colorant, and the like in a mixer such as a ball-mill, thereafter melt-kneading with a closed kneader or a single-screw or twin-screw extruder, cooling, pulverizing and classifying the product. Further, a fluidity improver and the like may be added to the surface of the toner as occasion demands. The weight-average particle size of the resulting toner is preferably from 3 to 15 xcexcm.
The toner for electrophotography of the present invention can be used alone as a developer, in a case where the fine magnetic material powder is contained. Alternatively, in a case where the fine magnetic material powder is not contained, the toner may be used as a nonmagnetic one-component developer, or the toner can be mixed with a carrier and used as a two-component developer.